1. Technical Field
The present invention relates to a wireless communication system in which a plurality of sub stations wirelessly communicate with each other via a center module.
2. Background Art
FIG. 11 is a diagram showing a packet configuration for communication in a conventional wireless communication system. Referring to FIG. 11, a normal mode and a manager mode in the conventional wireless communication system will be described. FIG. 11 (a) shows a packet configuration in a normal mode. FIG. 11 (b) shows a packet configuration in the manager mode. In any mode, packet communication is performed using a time division duplex (TDD) scheme. It is provided that the number of available channels (the number of frequency bands) is two.
In an example in FIG. 11 (a), each of a store personnel 1 and a store personnel 2 communicates with a kitchen in the normal mode. A channel 1 (f1 MHz) is allocated to the communication by the store personnel 1. A channel 2 (f2 MHz) is allocated to the communication by the store personnel 2. FIG. 11 (a) shows a state in which all the prepared two channels are used by the store personnel.
In such a situation, when a manager wishes to urgently call staff members, the manager operates a center module to set the communication mode to the manager mode. After the wireless communication system is set to the manager mode, the communication by the store personnel 1 is forcedly terminated and downlink slots having been used by the store personnel 1 is exclusively used by the manager as shown in FIG. 11 (b). Likewise, the communication by the store personnel 2 having been performed using the channel 2 is forcedly terminated, and the channel 2 having been used by the store personnel 2 is forcedly switched to the channel 1.
In such a conventional communication system, when the communication mode is set to the manager mode, the call by the manager exclusively uses the channel in a forced manner in order to secure the urgent call from the manager. Accordingly, if the communication mode is switched to the manager mode while the store personnel is communicating with the kitchen in the normal mode, the communication from the store personnel to the kitchen is forcedly terminated. Further, during the manager mode is selected, another staff member cannot make a call.